Mediated, Thin-Layer Cell, Coulometric Determination of Monomolecular Films of Trichlorosilane Viologen Derivatives at Gold and Nonconducting Surfaces

Article abstract of DOI:10.1021/ac00132a016

A thin-layer, mediated, coulometric titration method is developed for the determination of electroactive reagents immobilized at nonconducting surfaces.The method was used to verify the monomolecular quantities of N-methyl-N-(2-(trimethoxysilyl)ethyl)benzyl-4,4'-bipyridinium dichloride and of other viologen silane derivatives immobilized at gold electrodes.The direct electroreduction gave surface coverages on average 50percent smaller than those obtained by the mediated coulometric method.The lack of complete electroactivity of the surface-bound material in customary voltammetric experiments was confirmed spectrophotometrically.This unexpected characteristic is related to the interfacial structure of the silane layers of which some fragments appear to be passivating to the direct heterogeneous electron transfer.The high density of the lateral siloxane bridging groups in such areas was postulated to be responsible for this effect.The mediated double layer charging of an electrically unconnected, conducting interface is described and illustrated by two examples.